A film comprising a norbornene compound polymer is excellent in heat resistance, transparency, chemical resistance and low water absorption, and is therefore useful for optical parts, electric insulating parts, electric/electronic parts, sealants for electronic parts, medical equipment, or packaging materials.
In the field of electric/electronic technology in which norbornene compound polymers have some essential applications, recently, advanced functions of electronic appliances have come to require high-density electric wiring and high-definition structuring of display devices for high-speed electric signal transmission.
Accordingly, films for use in these applications are required to have dimensional stability, especially dimensional stability to temperature changes, namely, to have a low linear expansion coefficient, and concretely, they are required to have a linear expansion coefficient of lower than 50 ppm/° C.
Regarding norbornene compound polymer films having a low linear expansion coefficient, Patent References 1 and 2 report that, after an alkoxysilyl group-bearing norbornene compound is copolymerized and formed into a film, its linear expansion coefficient may be reduced to about 40 ppm/° C. by crosslinking reaction between the alkoxysilyl groups. However, in this method, the crosslinking operation to be attained by exposing the film to water vapor is troublesome and, in addition, the addition of a crosslinking promoter may cause coloration of the film and may detract from the film stability in high-temperature environments.
Accordingly, a norbornene compound polymer film having a low linear expansion coefficient not according to the method is desired.
There are many reports relating to retardation plates and retardation compensatory films produced by stretching and orienting a film of a cyclic olefin resin such as a norbornene-based resin, for the above-mentioned optical applications and others (for example, Patent References 3 to 8).
These patent references say that addition polymers of a norbornene monomer and addition copolymers thereof with ethylene or the like can also be used, in which, however, only ring-opening polymers of a norbornene monomer were actually formed into films and their effects were confirmed.
However, the ring-opening polymers of a norbornene compound have a glass transition temperature of not higher than 200° C., and their heat resistance is limited. In general, the double bond remaining after the ring-opening polymerization is hydrogenated, but even after hydrogenation, there still remains some but minor double bonds in the molecular chains, and when exposed to high temperatures, the polymers may often cause problems of coloration and the like.    Patent Reference 1: JP-A 2005-48060    Patent Reference 2: JP-A 2005-126514    Patent Reference 3: JP-A 5-2108    Patent Reference 4: JP-A 6-59121    Patent Reference 5: JP-A 2000-304920    Patent Reference 6: JP-A 2001-296422    Patent Reference 7: JP-A 2004-133209    Patent Reference 8: JP-A 2006-18212